1. Field of the Invention
The present invention relates generally to electrical wiring devices, and particularly to devices that have miswiring protection.
2. Technical Background
Electrical distribution systems that provide power to a house, building or some other facility include one or more breaker panels coupled to a source of AC power. Of course, the breaker panel distributes AC power to one or more branch electric circuits installed in the structure. The electric circuits may typically include one or more receptacle outlets and may further transmit AC power to one or more electrically powered devices, commonly referred to in the art as load circuits. The receptacle outlets provide power to user-accessible loads that include a power cord and plug, the plug being insertable into the receptacle outlet. However, certain types of faults have been known to occur in electrical wiring systems. Accordingly, each electric circuit typically employs one or more electric circuit protection devices.
Both receptacle wiring devices and electric circuit protective wiring devices are disposed in an electrically non-conductive housing. The housing includes electrical terminals that are electrically insulated from each other. Line terminals couple the wiring device to wiring that provides AC electrical power from the breaker panel. Load terminals are coupled to wiring that directs AC power to one or more electrical loads. Those of ordinary skill in the pertinent art will understand that the term “load” refers to an appliance, a switch, or some other electrically powered device. Load terminals may also be referred to as “feed-through” terminals because the wires connected to these terminals may be coupled to a daisy-chained configuration of receptacles or switches. The load may ultimately be connected at the far end of this arrangement. Referring back to the device housing, the load terminals may be connected to an electrically conductive path that is also connected to a set of receptacle contacts. The receptacle contacts are in communication with receptacle openings disposed on the face of the housing. This arrangement allows a user to insert an appliance plug into the receptacle opening to thereby energize the device.
As noted above, there are several types of electric circuit protection devices. For example, such devices include ground fault circuit interrupters (GFCIs), ground-fault equipment protectors (GFEPs), and arc fault circuit interrupters (AFCIs). This list includes representative examples and is not meant to be exhaustive. Some devices include both GFCIs and AFCIs. As their names suggest, arc fault circuit interrupters (AFCIs), ground-fault equipment protectors (GFEPs) and ground fault circuit interrupters (GFCIs) perform different functions. An arc fault typically manifests itself as a high frequency current signal. Accordingly, an AFCI may be configured to detect various high frequency signals and de-energize the electrical circuit in response thereto. A ground fault occurs when a current carrying (hot) conductor creates an unintended current path to ground. A differential current is created between the hot/neutral conductors because some of the current flowing in the circuit is diverted into the unintended current path. The unintended current path represents an electrical shock hazard. Ground faults, as well as arc faults, may also result in fire.
A “grounded neutral” is another type of ground fault. This type of fault may occur when the load neutral terminal, or a conductor connected to the load neutral terminal, becomes grounded. While this condition does not represent an immediate shock hazard, it may lead to serious hazard. As noted above, a GFCI will trip under normal conditions when the differential current is greater than or equal to approximately 6 mA. However, when the load neutral conductor is grounded the GFCI becomes de-sensitized because some of the return path current is diverted to ground. When this happens, it may take up to 30 mA of differential current before the GFCI trips. Therefore, if a double-fault condition occurs, i.e., if the user comes into contact with a hot conductor (the first fault) when simultaneously contacting a neutral conductor that has been grounded on the load side (the second fault), the user may experience serious injury or death.
One problem that is associated with protective devices relates to the protective device being miswired in the field by an installer. In particular, the installer connects the line terminals to the load side of the electric circuit, and connects the load terminals to the AC power source. Miswiring may result in the protective device not protecting the user from the fault conditions described above. Labels and installation instruction sheets have been used to prevent miswiring. However, instructive material may be ignored by an installer.
Another problem is that protective device, like all electrical devices, have a limited life expectancy. When the device has reached end of life, the user may not be protected from the fault condition. End of life failure modes include failure of device circuitry, the relay solenoid that opens the GFCI interrupting contacts, and/or the solenoid driving device, such as a silicon controlled rectifier. An end of life failure mode can result in the protective device not protecting the user from the faults referred to above. Test buttons have been incorporated into protective devices to provide the user with a means for testing the effectiveness of the device. One drawback to this approach lies in the fact that if the user fails to use the test button, the user will not know if the device is functional. Even if the test is performed, the test results may be ignored by the user for various reasons.
What is needed is a protective device configured to reliably protect the user from a fault condition in the electrical power distribution system. A protective device must be configured to detect, and indicate, that a miswire condition is extant. A protective device is further needed that denies power to the portion of the electrical power distribution system experiencing the fault condition. Further, a protective device is needed that is equipped to decouple the load terminals from the line terminals in the event of an end of life condition.